How do I remove multiple 404 crawl errors from Google Webmaster without using Webmaster Tools?

For pages that are no longer available:

• If the page is no longer available and receives no substantial traffic or connections, set the status code to 404 or 410. Make sure the server header response is 404 or 410 rather than 200.
• Each old page should be 301 redirected to a relevant, related page on your site.
• Do not send a large number of dead pages to your home page. They should either 404 or redirect to a comparable page.

• Make sure there's enough material on the page, as thin content can lead to a soft 404 error.
• While serving a 200 response code, be sure the content on your page does not appear to be a 404 page.

Read more : How do I resolve an unreachable issue in Webmaster Tools?